integrated services and differentiated services. limitations of ip architecture in supporting...
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Integrated Services Integrated Services and Differentiated and Differentiated
ServicesServices
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Limitations of IP Architecture Limitations of IP Architecture in Supporting Resource in Supporting Resource
ManagementManagement• IP provides only best effort service• IP does not participate in resource management
– Cannot provide service guarantees on a per flow basis– Cannot provide service differentiation among traffic
aggregates
• Early efforts– Tenet group at Berkeley (Ferrari and Verma)– ATM
• IETF efforts – Integrated services initiative– Differentiated services initiative
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Integrated Services InternetIntegrated Services Internet• Enhance IP’s service model
– Old model: single best-effort service class– New model: multiple service classes, including best-
effort and QoS classes
• Create protocols and algorithms to support new service models– Old model: no resource management at IP level– New model: explicit resource management at IP level
• Key architecture difference– Old model: stateless – New model: per flow state maintained at routers
• used for admission control and scheduling• set up by signaling protocol
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Integrated Services Network Integrated Services Network
• Flow or session as QoS abstractions
• Each flow has a fixed or stable path
• Routers along the path maintain the state of the flow
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Integrated Services Integrated Services ExampleExample
SenderReceiver
• Achieve per-flow bandwidth and delay guarantees– Example: guarantee 1MBps and < 100 ms delay to a flow
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Integrated Services Integrated Services ExampleExample
SenderReceiver
• Allocate resources - perform per-flow admission control
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Integrated Services Integrated Services ExampleExample
SenderReceiver
• Install per-flow state
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SenderReceiver
• Install per flow state
Integrated Services Integrated Services ExampleExample
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Integrated Services Integrated Services Example: Data PathExample: Data Path
SenderReceiver
• Per-flow classification
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Integrated Services Integrated Services Example: Data PathExample: Data Path
SenderReceiver
• Per-flow buffer management
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Integrated Services Integrated Services ExampleExample
SenderReceiver
• Per-flow scheduling
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How Things Fit Together How Things Fit Together
Admission Control
Data InData Out
Con
trol P
lan
eD
ata
Pla
ne
Scheduler
Routing Routing
MessagesRSVP
messages
Classifier
RSVP
Route Lookup
Forwarding Table Per Flow QoS Table
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Service ClassesService Classes
• Multiple service classes• Service can be viewed as a contract
between network and communication client– end-to-end service– other service scopes possible
• Three common services– best-effort (“elastic” applications)– hard real-time (“real-time” applications)– soft real-time (“tolerant” applications)
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Hard Real Time: Guaranteed Hard Real Time: Guaranteed ServicesServices
• Service contract– network to client: guarantee a deterministic
upper bound on delay for each packet in a session
– client to network: the session does not send more than it specifies
• Algorithm support– admission control based on worst-case analysis– per flow classification/scheduling at routers
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Soft Real Time: Controlled Soft Real Time: Controlled Load ServiceLoad Service
• Service contract:– network to client: similar performance
as an unloaded best-effort network– client to network: the session does not
send more than it specifies
• Algorithm Support– admission control based on
measurement of aggregates– scheduling for aggregate possible
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RSVP Usage and Related IsRSVP Usage and Related Issuessues
1616
Role of RSVP in the Role of RSVP in the ArchitectureArchitecture
• Signaling protocol for establishing per flow state
• Carry resource requests from hosts to routers
• Collect needed information from routers to hosts
• At each hop– consults admission control and policy module– sets up admission state or informs the
requester of the failure
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RSVP Design FeaturesRSVP Design Features
• IP Multicast centric design• Receiver initiated reservation• Different reservation styles• Soft state inside network• Decouple routing from reservation
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IP MulticastIP Multicast
• Best-effort MxN delivery of IP datagrams • Basic abstraction: IP multicast group
– identified by Class D address: 224.0.0.0 - 239.255.255.255
– sender needs only to know the group address, but not the membership
– receiver joins/leaves group dynamically
• Routing and group membership managed distributedly– no single node knows the membership– tough problem– various solutions: DVMRP, CBT, PIM
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RSVP Reservation ModelRSVP Reservation Model
• Performs signaling to set up reservation state for a session
• A session is a simplex data flow sent to a unicast or a multicast address, characterized by– <IP dest, protocol number, port
number>
• Multiple senders and receivers can be in session
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RSVP Usage and Related IsRSVP Usage and Related Issuessues
2020
The Big PictureThe Big Picture
NetworkSender
Receiver
PATH Msg
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RSVP Usage and Related IsRSVP Usage and Related Issuessues
2121
The Big Picture (2)The Big Picture (2)
NetworkSender
Receiver
PATH Msg
RESV Msg
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RSVP Basic OperationsRSVP Basic Operations
• Sender sends PATH message via the data delivery path– set up the path state each router including the
address of previous hop
• Receiver sends RESV message on the reverse path– specifies the reservation style, QoS desired– set up the reservation state at each router
• Things to notice– receiver initiated reservation– decouple the routing from reservation– two types of state: path and reservation
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Route PinningRoute Pinning• Problem: asymmetric routes
– You may reserve resources on RS3S5S4S1S, but data travels on SS1S2S3R !
• Solution: use PATH to remember direct path from S to R, I.e., perform route pinning
S1S1
S2S2
S3S3
SSRR
S5S5S4S4PATH
RESV
IP routing
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PATH and RESV messagesPATH and RESV messages
• PATH also specifies – Source traffic characteristics
• use token bucket
– Reservation style – specify whether a RESV message will be forwarded to this server
• RESV specifies – Queueing delay and bandwidth requirements – Source traffic characteristics (from PATH)– Filter specification, i.e., what senders can use
reservation– Based on these routers perform reservation
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Token BucketToken Bucket• Characterized by two parameters (r, b)
– r – average rate– b – token depth
• Assume flow arrival rate <= R bps (e.g., R link capacity)• A bit is transmitted only when there is an available token• Arrival curve – maximum amount of bits transmitted by time t
r bps
b bits
<= R bps
regulatortime
bits
b
slope R
slope r
Arrival curve
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End-to-End ReservationEnd-to-End Reservation• When R gets PATH message it knows
– Traffic characteristics (tspec): (r,b,R)– Number of hops
• R sends back this information + worst-case delay in RESV• Each router along path provide a per-hop delay guarantee
and forward RESV with updated info – In simplest case routers split the delay
S1S1
S2S2
S3S3
SSRR(b,r,R) (b,r,R,3)
num hops
(b,r,R,2,D-d1)(b,r,R,1,D-d1-d2)(b,r,R,0,0)
(b,r,R,3,D)
worst-case delayPATH
RESV
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Per-hop ReservationPer-hop Reservation
• Given (b,r,R) and per-hop delay d• Allocate bandwidth ra and buffer space Ba
such that to guarantee d
bits
b
slope rArrival curve
d
Ba
slope ra
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Reservation StyleReservation Style
• Motivation: achieve more efficient resource utilization in multicast (M x N)
• Observation: in a video conferencing when there are M senders, only a few can be active simultaneously– multiple senders can share the same
reservation
• Various reservation styles specify different rules for sharing among senders
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Reservation Styles and Filter Reservation Styles and Filter SpecSpec
• Reservation style– use filter to specify which sender can use the
reservation
• Three styles– wildcard filter: does not specify any sender; all
packets associated to a destination shares same resources
• Group in which there are a small number of simultaneously active senders
– fixed filter: no sharing among senders, sender explicitly identified for the reservation
• Sources cannot be modified over time
– dynamic filter: resource shared by senders that are (explicitly) specified
• Sources can be modified over time
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Wildcard Filter ExampleWildcard Filter Example• Receivers: H1, H2; senders: H3, H4, H5• Each sender sends B• H1 reserves B; listen from one server at a time
S1S1 S2S2 S3S3
H2H2
H1H1
H5H5
H4H4
H3H3
(B,*)(B,*) (B,*)
(B,*)
(B,*)
(B,*)
senderreceiver
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Wildcard Filter ExampleWildcard Filter Example
• H2 reserves B
S1S1 S2S2 S3S3
H2H2
H1H1
H5H5
H4H4
H3H3
(B,*)(B,*) (B,*)
senderreceiver
(B,*)
(B,*) (B,*)
(B,*)
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Wildcard FilterWildcard Filter
• Advantages– Minimal state at routers
• Routers need to maintain only routing state augmented by reserved bandwidth on outgoing links
• Disadvantages – May result in inefficient resource utilization
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Wildcard Filter: Inefficient Wildcard Filter: Inefficient Resource Utilization Resource Utilization
ExampleExample• H1 reserves 3B; wants to listen from
all senders simultaneously• Problem: reserve 3B on (S3:S2)
although 2B sufficient !
S1S1 S2S2 S3S3
H2H2
H1H1
H5H5
H4H4
H3H3
(3B,*)(3B,*) (3B,*)
senderreceiver
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Fixed Filter ExampleFixed Filter Example• Receivers: H2, H3, H4, H4; Sender: H1, H4, H5• Routers maintain state for each receiver in the
routing table
S1S1 S2S2 S3S3
H2H2
H1H1
H3H3
senderreceiver
H5
H4
sender+receiver
NextHop Sources H1 S2(H5, H4) H2 H1(H1), S2(H5, H4)
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Fixed Filter ExampleFixed Filter Example
• H2 wants to receive B only from H4
S1S1 S2S2 S3S3
H2H2
H1H1
H3H3
senderreceiver
H5
H4
sender+receiver
(B,H4)
(B,H4) (B,H4)
(B,H4)
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Dynamic Filter ExampleDynamic Filter Example
• H5 wants to receive 2B from any source
S1S1 S2S2 S3S3
H2H2
H1H1
H3H3
senderreceiver
H5
H4
sender+receiver
(B,H4) (B,H4)
(B,H4)(2B,*)
(B,H4)(B,*)
(B,*)
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Tire-down Example Tire-down Example
• H4 leaves the group– H4 no longer sends PATH message– State corresponding to H4 removed
S1S1 S2S2 S3S3
H2H2
H1H1
H3H3
senderreceiver
H5
H4
sender+receiver
(B,H4) (B,H4)
(B,H4)(2B,*)
(B,H4)(B,*)
(B,*)
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Tire-down Example Tire-down Example
• H4 leaves the group– H4 no longer sends PATH message– State corresponding to H4 removed
S1S1 S2S2 S3S3
H2H2
H1H1
H3H3
senderreceiver
H5
sender+receiver
(2B,*)
(B,*)
(B,*)
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Fixed Filter ExampleFixed Filter Example
• Receivers: H2, H3, H4, H4; Sender: H1
S1S1 S2S2 S3S3
H2H2
H1H1
H5H5
H4H4
H3H3
(*,B)(*,B) (*,B)
(*,B)
(*,B)
(*,B)
senderreceiver
(*,B)
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Soft StateSoft State• Per session state has a timer associated with it
– path state, reservation state
• State lost when timer expires• Sender/Receiver periodically refreshes the state,
resends PATH/RESV messages, resets timer• Claimed advantages
– no need to clean up dangling state after failure– can tolerate lost signaling packets
• signaling message need not be reliably transmitted
– easy to adapt to route changes
• State can be explicitly deleted by a Teardown message
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RSVP and RoutingRSVP and Routing• RSVP designed to work with variety of routing
protocols• Minimal routing service
– RSVP asks routing how to route a PATH message
• Route pinning– addresses QoS changes due to “avoidable” route
changes while session in progress
• QoS routing– RSVP route selection based on QoS parameters– granularity of reservation and routing may differ
• Explicit routing– Use RSVP to set up routes for reserved traffic
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Recap of RSVPRecap of RSVP
• PATH message– sender template and traffic spec– advertisement– mark route for RESV message– follow data path
• RESV message– reservation request, including flow and filter spec– reservation style and merging rules– follow reverse data path
• Other messages– PathTear, ResvTear, PathErr, ResvErr
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QuestionQuestion
• What do you think about the design decision to make RSVP IP multicast centric?
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What is still Missing?What is still Missing?
• Classification algorithm• Scheduling algorithm• Admission control algorithm• QoS Routing algorithm
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Differentiated Differentiated ServicesServices
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What is the Problem?What is the Problem?
• Goal: provide support for wide variety of applications:– Interactive TV, IP telephony, on-line
gamming (distributed simulations), VPNs, etc
• Problem: – Best-effort cannot do it (see previous
lecture)– Intserv can support all these applications,
but• Too complex• Not scalable
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Differentiated Services Differentiated Services (Diffserv)(Diffserv)
• Build around the concept of domain• Domain – a contiguous region of network under
the same administrative ownership• Differentiate between edge and core routers• Edge routers
– Perform per aggregate shaping or policing– Mark packets with a small number of bits; each bit
encoding represents a class (subclass)
• Core routers– Process packets based on packet marking
• Far more scalable than Intserv, but provides weaker services
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Diffserv ArchitectureDiffserv Architecture• Ingress routers
– Police/shape traffic– Set Differentiated Service Code Point (DSCP) in Diffserv (DS)
field
• Core routers– Implement Per Hop Behavior (PHB) for each DSCP– Process packets based on DSCP
IngressEgressEgress
IngressEgressEgress
DS-1 DS-2
Edge router Core router
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Differentiated Service (DS) Differentiated Service (DS) FieldField
Version HLen TOS Length
Identification Fragment offsetFlags
Source address
Destination address
TTL Protocol Header checksum
0 4 8 16 19 31
Data
IPheader
• DS filed reuse the first 6 bits from the former Type of Service (TOS) byte
• The other two bits are proposed to be used by ECN
DS Filed0 5 6 7
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Differentiated ServicesDifferentiated Services
• Two types of service– Assured service– Premium service
• Plus, best-effort service
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Assured ServiceAssured Service[Clark & Wroclawski ‘97][Clark & Wroclawski ‘97]
• Defined in terms of user profile, how much assured traffic is a user allowed to inject into the network
• Network: provides a lower loss rate than best-effort– In case of congestion best-effort packets
are dropped first
• User: sends no more assured traffic than its profile– If it sends more, the excess traffic is
converted to best-effort
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Assured ServiceAssured Service• Large spatial granularity service• Theoretically, user profile is defined irrespective of
destination– All other services we learnt are end-to-end, i.e., we know
destination(s) apriori
• This makes service very useful, but hard to provision (why ?)
Ingress
Traffic profile
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Premium ServicePremium Service[Jacobson ’97][Jacobson ’97]
• Provides the abstraction of a virtual pipe between an ingress and an egress router
• Network: guarantees that premium packets are not dropped and they experience low delay
• User: does not send more than the size of the pipe– If it sends more, excess traffic is delayed, and
dropped when buffer overflows
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Edge RouterEdge Router
Classifier
Traffic conditioner
Traffic conditioner
Scheduler
Class 1
Class 2
Best-effort
Marked traffic
Ingress
Per aggregateClassification (e.g., user)
Data traffic
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AssumptionsAssumptions
• Assume two bits – P-bit denotes premium traffic– A-bit denotes assured traffic
• Traffic conditioner (TC) implement– Metering– Marking– Shaping
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TC Performing TC Performing Metering/MarkingMetering/Marking
• Used to implement Assured Service• In-profile traffic is marked:
– A-bit is set in every packet• Out-of-profile (excess) traffic is unmarked
– A-bit is cleared (if it was previously set) in every packet; this traffic treated as best-effort
r bps
b bits
Metering in-profile traffic
out-of-profile traffic
assured traffic
User profile (token bucket)
Set A-bit
Clear A-bit
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TC Performing TC Performing Metering/Marking/ShapingMetering/Marking/Shaping
• Used to implement Premium Service• In-profile traffic marked:
– Set P-bit in each packet
• Out-of-profile traffic is delayed, and when buffer overflows it is dropped
r bps
b bits
Metering/Shaper/Set P-bit
in-profile traffic
out-of-profile traffic(delayed and dropped)
premium traffic
User profile(token bucket)
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SchedulerScheduler• Employed by both edge and core routers• For premium service – use strict priority, or weighted
fair queuing (WFQ)• For assured service – use RIO (RED with In and Out)
– Always drop OUT packets first• For OUT measure entire queue• For IN measure only in-profile queue
OUT IN
Average queue length
1
Droppingprobability
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Scheduler ExampleScheduler Example
• Premium traffic sent at high priority• Assured and best-effort traffic pass
through RIO and then sent at low priority
P-bit set?
A-bit set? RIO
yes
noyes
no
high priority
low priority
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Control PathControl Path
• Each domain is assigned a Bandwidth Broker (BB)– Usually, used to perform ingress-egress
bandwidth allocation
• BB is responsible to perform admission control in the entire domain
• BB not easy to implement– Require complete knowledge about domain– Single point of failure, may be performance
bottleneck– Designing BB still a research problem
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ExampleExample
• Achieve end-to-end bandwidth guarantee
BBBB BBBB BBBB1
2 3
579
sender
receiver8 profile 6
profile4 profile
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Comparison to Best-Effort Comparison to Best-Effort and Intservand Intserv
Best-Effort Diffserv Intserv
Service ConnectivityNo isolationNo guarantees
Per aggregate isolationPer aggregate guarantee
Per flow isolationPer flow guarantee
Service scope
End-to-end Domain End-to-end
Complexity No setup Long term setup Per flow steup
Scalability Highly scalable (nodes maintain only routing state)
Scalable(edge routers maintains per aggregate state; core routers per class state)
Not scalable (each router maintains per flow state)
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SummarySummary
• Diffserv more scalable than Intserv– Edge routers maintain per aggregate state– Core routers maintain state only for a few traffic
classes
• But, provides weaker services than Intserv, e.g.,– Per aggregate bandwidth guarantees (premium
service) vs. per flow bandwidth and delay guarantees
• BB is not an entirely solved problem– Single point of failure– Handle only long term reservations (hours, days)